A simplex sheet is a sheet intended to be printed on one side. A duplex sheet is a sheet intended to be printed on both sides. In most cases a speciality sheet is meant to be printed on one side only, however a speciality sheet may be a duplex sheet.
A mixed-plex print job is a print job that comprises simplex sheets as well as duplex sheets.
A normal sheet is defined as a non-speciality sheet, for which the front side can be processed in the same way as the back side.
Turn stations as such are assumed to be known from the prior art and are therefore not elaborated upon.
According to the paper path of a printing system each of the plurality of sheets is transported from an input section of the printing system towards a print engine comprising a print head or a print assembly. By means of the print head or print assembly marking material is disposed on each of the plurality of sheets. The marking material may be ink which has to be dried or to be UV-cured, or a toner which has to be fused to the sheets. Each of the plurality of sheets is guided from the print head or print assembly towards an output section comprising at least one output holder. In order to enable duplex printing the paper path contains a loop, a so-called duplex loop. A sheet enters the loop in a first pass in order to print image data on one side of the sheet, goes through the duplex loop and enters the duplex loop in a second pass in order to print image data on the other side of the sheet. Therefore the duplex loop comprises a first turn station to turn the sheets that need to be printed on the back side of the sheet.
After a sheet has been printed upon on both sides, the sheet is transported to the output section for further finishing. A print engine with a duplex loop may have a print speed of twice as high as a speed of a separation in the input module and a working speed of an output module or finisher. In such a case the duplex loop may be used to print on the plurality of sheets by interweaving the plurality of sheets in the first pass and in the second pass. The present invention is also applicable in a print mode wherein a plurality of sheets is firstly printed on one side in the first pass, and secondly the plurality is printed on the second side in the second pass, also known as a burst print mode. Duplex sheets that need to be printed on the back side of the sheet are turned by the first turn station, for example in a feed direction of the sheet such that a trailing edge of a sheet in the paper path becomes a leading edge of the sheet in the paper path. The first turn station may be configured to turn the sheet in a direction perpendicular to the feed direction. Sheets that are one-sided printed in the first pass may be interweaved with sheets that need to be printed on the front side in the duplex loop just before the print engine.
Sheets are handled in the order as the sheets are also deposited in the output holder.
The logic module in the control unit may use information about the sheets derived from the print job properties per page of the print job, knowledge of the type of sheets provided in the input holders, and/or input from sensors positioned in the input holders and/or in the paper path which are able to sense the type of sheets. A print job property may be a print medium type property and additional information about the print medium type may be retrieved from a media database available in memory of the control unit.
In the printing system according to the present invention, speciality sheets may be printed upon only on one side due to paper path constraints or due to media constraints. For example, a tab sheet may not be turned in the feeding or transport direction because an extending tab of the tab sheet needs to be kept on the trailing edge because of runability and sheet positioning in the paper path. When a duplex job with normal sheets and speciality sheets is scheduled in the scheduler duplex sheets may be printed by means of the duplex loop and the first turn station, but for printing a speciality sheet of the print job the duplex loop has to be emptied, which results in an unproductive system when printing speciality sheets tabs in combination with duplex sheets and keeping a print order.
It is an object of the present invention to provide a printing system that permits printing of duplex sheets in combination with speciality sheets in a productive way.